Continuous centrifuge

ABSTRACT

A centrifuge ( 1 ) for continuously separating a fluid stream into fractions of different density comprising: 
         conduit means ( 17 ) for radially directing flow of the fluid stream,    drive means ( 19, 22 ) for rotating the conduit means about an axis ( 19 ) whereby to subject the fluid stream to centrifugal force causing it to travel from a location in the conduit means nearer to the axis to a position further away from the axis, and    a plurality of conduit outlets ( 35, 36, 37 ) from the conduit means arranged at different radial distances from the axis for taking off fractions of different density from the fluid stream.

FIELD OF THE INVENTION

This invention relates to a continuous centrifuge. It relatesspecifically but not exclusively to a continuous centrifuge which iscapable of separating a plurality of fractions from a fluid stream andto methods for separating such fractions.

BACKGROUND OF THE INVENTION

Centrifuges have long been used to separate fluids containing componentshaving different densities. In one of the most common forms ofcentrifuge design, a fluid sealed in a container is rotated at highspeed by a radial arm to generate a high degree of centripetalacceleration within the fluid. This centripetal acceleration accentuatesthe effect of differing densities in the fluid to cause the highestdensity components of the fluid to settle at a point radially outermostwith the lower density components settling within the container in bandsmore radially inward.

Whilst such centrifuges are effective in providing separation of fluidsinto density layers, they suffer from a major disadvantage in that theyrequire stop/start operation ie. each individual container needs to befilled and then attached to the centrifuge arm which initially must bestationary. The centrifuge is then speeded up from rest and operateduntil the various layers settle. It then needs to be stopped and thecontainer holding the separated layers is removed. The layers areindividually drained from the container. The whole process is repeatedstep by step until all the material required is separated.

Clearly this approach is inefficient both in terms of the handlinginvolved and also in terms of the energy wasted in stopping and startingthe centrifuge. It is also limited in relation to the rate at whichmaterial can be separated given the stop/start nature of the operation.

It is therefore an object of the invention to provide a centrifuge andmethod for operating same which ameliorates one or more of the aforesaiddisadvantages of centrifuge designs.

DISCLOSURE OF THE INVENTION

The invention provides in one aspect a centrifuge for continuouslyseparating a fluid stream into fractions of different densitycomprising:

conduit means for radially directing flow of the fluid stream,

drive means for rotating the conduit means about an axis whereby tosubject the fluid stream to centrifugal force causing it to travel froma location in the conduit means nearer to the axis to a position furtheraway from the axis, and

a plurality of conduit outlets from the conduit means arranged atdifferent radial distances from the axis for taking off fractions ofdifferent density from the fluid stream.

The conduit means may comprise two or more hollow arms. The hollow armsmay be arranged so that the centrifugal force exerted by the arms issubstantially balanced about the axis.

In a preferred aspect of the invention, there are two opposed arms. Theymay be in the form of pinch sluices.

The conduit outlets are suitably arranged in a wall of the conduit. Theymay be arranged at the bottom and/or side walls of the conduit. They maybe adjusted in size so as to regulate the rate of discharge of afraction of the fluid stream from the respective outlets. The conduitoutlets may be arranged to discharge the fractions into a launder.

Suitably, the launder is provided with one or more baffles to defineseparate regions for receiving the individual discharges from theconduit outlets. The baffles may be concentric. The launder may also beprovided with a sloping floor. Launder outlets may be arranged near alower portion of the sloping floor. Individual launder outlets may beprovided to correspond to each of the conduit outlets.

The fluid stream may be directed to the conduit means via a centrallylocated feed tube assembly. The feed tube assembly may incorporate adistribution chamber arranged to direct the fluid stream into arms ofthe conduit means.

The distribution chamber may direct the fluid stream at a region nearthe bottom surface of the pinch sluices comprising the conduit means.

Suitably the feed tube assembly includes one or more overflow tubes. Theoverflow tubes may direct overflow fluid stream into a central portionof the launder. The overflow fluid stream may be recycled to thecentrifuge.

In another aspect the invention provides a method of continuouslyseparating a fluid stream into fractions of different density comprisingremoving fractions of the fluid stream from a conduit means rotatingabout an axis, at varying distances away from the axis.

The invention also provides methods of separating fluid streamscomprising subjecting the fluid streams to separation by centrifuges ashereinbefore defined.

Typical examples of fluid streams which may be separated using thecentrifuge include slurries containing gold mineralisation, tantalumores, tin ores, iron ores, coal, mineral sands, copper ores, silver,diamonds, zinc and lead. The invention may even be used for recyclingoperations such as the separation of plastic scrap from metal scrap.Needless to say, the range of fluids which may be separated is quitelarge and not limited to those specifically exemplified.

Preferred aspects of the invention will now be described with referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an isometric view of a centrifuge according to theinvention;

FIG. 2 shows a plan view of the centrifuge of FIG. 1;

FIG. 3 shows an elevation taken through the vertical section A-A of FIG.2;

FIG. 4 shows an enlarged view of a part of a feed tube assembly;

FIG. 5 shows a plan view of a section of conduit; and

FIG. 6 shows an elevation of the section of conduit of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The various elements identified by numerals in the drawings are listedin the following integer list.

INTEGER LIST

-   1 Centrifuge-   3 Launder assembly-   5 Base frame assembly-   7 Feed tube assembly-   8 Inlet-   9 Overflow tube-   11 Flange-   13 Flange-   15 Distribution chamber-   17 Conduit section/pinch sluice-   19 Drive shaft-   20 Bearing-   22 Motor-   23 Circular outer wall-   24 Sloping floor-   25 Concentric baffles-   27 Outlet-   28 Outlet-   29 Outlet-   30 Outlet-   32 Flange-   34 Inlet-   35 Outlet-   36 Outlet-   37 Outlet-   39 Mounting plate-   40 Mounting plate-   41 Mounting plate-   42 Restriction orifice

Referring to FIGS. 1 to 6 of the accompanying drawings, there is shown acentrifuge generally designated 1 for performing the invention.

The centrifuge comprises a launder assembly 3 mounted on a base frameassembly 5.

A rotatable feed tube assembly 7 is arranged centrally in the launderand includes an inlet 8 through which a fluid stream may be directed.

The feed tube assembly includes two overflow tubes 9 which are arrangedto direct overflow fluid stream into a central portion of the launder.Flanges 11 and 13 are provided so as to facilitate joining of thedistribution chamber 15 to the upper part of the feed tube assembly.

The distribution chamber is arranged so as to direct the fluid streaminto the conduit sections 17 attached thereto. The conduit sections arein the form of pinch sluices in the illustrated embodiment. Howeverother forms of conduits having a wide variety of shapes may be useddepending upon the nature of the fluid stream. It is even possible tohave a completely circular conduit extending around the distributionchamber.

A drive shaft 19 for rotating the feed tube assembly and attachedconduit sections connects to the bottom of the distribution chamber 15.The drive shaft is mounted via the bearings 20 which in turn are mountedon the base frame assembly 5.

An electric motor 22 and associated conventional gearing/pulleys (notshown) rotates the drive shaft 19 and hence the feed tube assembly andassociated conduit sections.

The launder assembly comprises a circular outer wall 23 attached to asloping floor 24.

A number of concentric circular baffles 25 are provided so as to definea series of annular channels for receiving fluid stream directed fromthe conduit sections 17. Outlets 27, 28 and 29 are provided at a lowerpoint on the sloping floor for tapping the separated fractions receivedin each of the annular channels.

A further outlet 30 is provided for the outer most of the annularchannels.

The conduit sections 17 shown in more detail in FIGS. 5 and 6 are in theform of pinch sluices. They include a flange 32 to facilitate attachmentvia a corresponding flange on the distribution chamber.

An inlet 32 is provided at a position proximate the floor of the pinchsluice so that the fluid stream enters into a position near the floorand is pushed upwardly as it moves radially outwardly along the pinchsluice. It is anticipated that an arrangement of inlet in this positionshould tend to have the effect of concentrating heavier materials nearthe base of the sluice. However, it is to be appreciated that the inletmay be arranged higher to get different effects in relation to thedistribution of the different fractions as they move through the sluice.

The configuration of the pinch sluice, moving from a position radiallyinwardly to a position radially outwardly, begins with a broad butthinner conduit area tapering to a narrow but much thicker area radiallyoutwardly therefrom to a location near its radially outermost point.From this position it again widens and reduces in thickness or depth asit approaches the radially outermost point.

A series of outlets 35, 36 and 37 are provided at radially differentpositions along the length of the pinch sluice. Whilst they are shown tobe on the bottom surface of the pinch sluice in the drawings, it is tobe appreciated that the openings may also or alternatively extendthrough the sides of the sluice depending upon the nature of the fluidstream and the type of separation required. Furthermore, whilst thedrawings show the sides of the sluice as being formed of planar sheets,it is to be appreciated that the walls may be curved. Thus, if theoutlets extend along the sides of the walls, it is to be anticipatedthat a more curved base/side wall arrangement may be used than the oneshown in the drawings.

Mounting plates 39, 40 and 41 are provided immediately beneath each ofthe outlets 35, 36 and 37. These mounting plates are provided so as toallow restriction orifices of different sizes to be mounted thereon. Anexample of one form of restriction orifice 42 having an extended tubewhich protrudes below the level of the baffles 25 is shown in dottedoutline separated from and below outlet 35 in FIG. 6. Thus, by choosinga particular size of restriction orifice, it is possible to regulate theamount of fluid stream tapped at each outlet. This in turn can have aneffect on the nature of the fraction selected from the fluid stream.

The centrifuge can be operated continuously by feeding a constant streamof slurry into the inlet 8. The slurry passes into the distributionchamber 15 from whence the rotary motion of the distribution chamber andassociated conduit sections 17 cause the slurry to be accelerated intoand along the conduit section. A high rotation speed generates a highdegree of centrifugal force to move the fluid stream. This has theeffect of speeding separation of the different density components of theslurry. Different density fractions can be continuously expelled throughthe outlets 35, 36 and 37 into the concentric channels and hence out ofthe outlets 27, 28, 29 and 30 on a continuous basis.

Clearly, an apparatus and method in accordance with the invention can beoperated continuously at a far greater rate than the stop and startprocesses hereinbefore described in relation to prior art devices.

Whilst the above description includes the preferred embodiments of theinvention, it is to be understood that many variations, alterations,modifications and/or additions may be introduced into the constructionsand arrangements of parts previously described without departing fromthe essential features or the spirit or ambit of the invention.

It will be also understood that where the word “comprise”, andvariations such as “comprises” and “comprising”, are used in thisspecification, unless the context requires otherwise such use isintended to imply the inclusion of a stated feature or features but isnot to be taken as excluding the presence of other feature or features.

The reference to any prior art in this specification is not, and shouldnot be taken as, an acknowledgment or any form of suggestion that suchprior art forms part of the common general knowledge.

1. A centrifuge for continuously separating a fluid stream intofractions of different density comprising: conduit means for radiallydirecting flow of the fluid stream, drive means for rotating the conduitmeans about an axis whereby to subject the fluid stream to centrifugalforce causing it to travel from a location in the conduit means nearerto the axis to a position further away from the axis, and a plurality ofconduit outlets from the conduit means arranged at different radialdistances from the axis for taking off fractions of different densityfrom the fluid stream.
 2. The centrifuge of according to claim 1 whereinthe conduit means comprise a plurality of hollow arms extending radiallywith respect to the axis so that the centrifugal force exerted by thearms is substantially balanced about the axis.
 3. The centrifugeaccording to claim 2 wherein the conduit means comprise two pinchsluices.
 4. The centrifuge according to claim 1 wherein the conduitoutlets are adjustable to vary the rate of fluid flow therethrough. 5.The centrifuge according to claim 1 wherein the conduit outlets arearranged to discharge the fractions into a launder.
 6. The centrifugeaccording to claim 5 wherein the launder is provided with at least onebaffle to define separate regions for receiving discharges from theconduit outlets.
 7. The centrifuge according to claim 6 wherein there ismore than one baffle and the baffles are concentric.
 8. The centrifugeaccording to claim 5 wherein the launder has a sloping floor.
 9. Thecentrifuge according to claim 8 wherein the outlets from the launder areprovided proximate the lower most level of the sloping floor and aseparate launder outlet is provided to correspond to each conduitoutlet.
 10. The centrifuge according to claim 1 comprising adistribution chamber for directing the fluid stream into the conduitmeans the distribution chamber being located on the axis.
 11. Thecentrifuge according to claim 10 wherein the conduit means comprise apair of pinch sluices and the distribution chamber is arranged to directthe fluid stream into a region near the bottom of one end of the pinchsluices.
 12. The centrifuge according to claim 1 comprising, a feed tubeassembly including a distribution chamber for directing the fluid streaminto the conduit means, and one or more overflow tubes for directingoverflow fluid stream to a central portion of a launder locatedunderneath the conduit means.
 13. A method of continuously separating afluid stream into fractions of different density comprising removingfractions of the fluid stream from conduit means rotating about an axis,at varying distances away from the axis by subjecting the fluid streamto separation by a centrifuge as defined in claim
 1. 14-16. (canceled)